The invention relates to atmospheric cooling towers of the kind comprising a vertical chimney or cup providing buoyancy or draft, a distributor supplied with water flowing from the distributor and dispersing it in currents streaming down over a packing having no gap in the circumferential direction and a basin for collecting the water cooled by contact with an air flow penetrating through openings in the lower part of the chimney and rising through this latter.
Cooling towers of this type are known (French Pat. No. 2,459,437). They are more and more widely used in power stations other than those situated on the coast for the delivery rate which rivers can supply is frequently insufficient for cooling the condenser of a high power thermal power station without an excessive rise in temperature. The absence of gaps, such as those provided in U.S. Pat. No. 3,846,519 allows the thermal power which may be removed by the cooling tower to be kept at a higher value.
In these cooling towers, frequently qualified as wet, the water is cooled by direct convection and by evaporation of a fraction of the flow, which increases the water vapor content of the air. Partial condensation of vapor at the outlet of the chimney causes a vapor cloud. This cloud is visible at a very great distance under certain atmospheric conditions, especially in the case of high power cooling towers whose chimney has a height and a diameter of the order of 100 meters. In addition, the discharge of a large airflow having a water vapor content close to saturation may cause frost and ice to form in the vicinity. These harmful effects are even more troublesome when the cooling tower is of small height, with natural or forced draft.
In an attempt to overcome the problem, French Pat. No. 2,459,437 discloses a tower which comprises dry air passages formed directly in the elements over which the water streams, but only in such elements. Water inevitably enters into the dry air passages and the advantages to be gained are quite limited. A cooling tower according to French Pat. No. 2,409,481 comprises a "contact body" in which dry air flow passages are formed. The passages do not extend beyond the zone where sprinkling and streaming occur, in the case of a countercurrent cooling tower. A complex construction must be provided for preventing water coming from the sprinkling or spraying nozzles from entering the dry air passages. And the fact that the ducts do not extend downwardly out of the "contact body" causes humidification of the dry air.
It is an object of the invention to provide a cooling tower in which the discharged air has a lower hygrometric content than in prior wet cooling towers and the steam cloud is reduced in volume.
To this end, there is provided a cooling tower of the above-defined type which comprises a two dimensional network of passages for flowing dry air from intake openings of the tower to a zone in the chimney situated beyond the streaming zone, the passages being placed so that their surface is swept by water to be cooled. The fact that the dry air passages convey air from openings provided at the lower part of the chimney to a zone in the chimney situated beyond the streaming zone avoids ingress of water into the air passages.
The invention may be implemented either during the construction of a cooling tower or by adapting an already existing cooling tower, with relatively small modifications. Furthermore, the invention is applicable to crossed current cooling towers as well as to counter current cooling towers.
The air circulation passages may consist of ducts which form a "dry" heat exchanger which may be placed in parallel with the "wet" exchanger where direct contact of the air and the streaming water occurs; it may as well be in series relation with the wet exchanger.
In a crossed current exchanger for example, the ducts will be disposed substantially radially to the axis of the tower and between beds of slats and will extend radially from openings of the tower to beyond a circular trough for distributing the water to be cooled over the packing in the case of a parallel flow arrangement; for series mounting, the ducts, which may again be disposed substantially radially, may extend through an annular chamber through which water to be cooled flows before it is delivered to a circular trough for spraying water over the slats.
In a counter current exchanger, the ducts may be placed substantially vertically and project through the packing from underneath the packing to beyond the channels for distributing water to be cooled.
The invention will be better understood from the following description of particular embodiments given by way of examples only.